Opioid analgesia can actually INCREASE sensitivity to pain in some cases
The exact cause is unclear, but may be due to up-regulation of NDMA receptors in spinal cord dorsal horn neurons
Pain tends to be DIFFERENT and DIFFUSE from the underlying condition for which the narcotics were prescribed
Switching from shorter acting opiates to methadone may be effective, as it is a weak NDMA antagonist and has only partial cross tolerance with other opioids
References
Gussow, L. Toxicology Rounds. When Opioids Increase Pain. Emergency Medicine News Feb 2013. 35(2):6.
